Intelligence transmission system



Dec. 25, 1945.

G. L. FREDENDALL 2,391,776 INTELLIGENCE TRANSMISSION SYSTEM Filed May29, 1945 2 Sheets-Sheet l T il..

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IN V EN TOR.

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INTELLIGENCE TRANSMISS ION SYSTEM Filed May 29, 1945 2 Sheets-Sheet 2T'l-- 1 I+ am .I1

IN V EN TOR.

G/ordon/ Z. Fredendall BY #S/@W A T rop/ver.

Patented Dec. 25, 1945 INTELLIGENCE TRANSMISSION SYSTEM Gordon L.Fredendall, Feasterville, Pa., asslgnor to Radio Corporation of America,a corporation of Delaware Application May 29, 1943, Serial No. 488,969

(Cl. Z50-27) 6 Claims.

The present invention relates to the art of signaling, and moreparticularly to a novel device and method applicable in the transmissionand reception of intelligence by signal impulses of varying timeduration.

Sound or video signals may be transmitted by modulating a carrier insuch a manner that the carrier itself may have constant amplitude andfrequency but will be varied as by keying on and off. A system ofpicture transmission is shown in Patent No. 2,083,245, granted June 8,1937, to Shore et al. A copending application of G. L. Fredendall etal., Serial No. 488,968, led May 29, 1943, discloses the transmission ofsound by means of derived signal impulses of varying duration. Thepresent invention provides a. novel method of and apparatus forconverting impulse signals derived, for example, by methods set forth inthe Shore patent or in the above noted application into the form of thesignals from which they were derived.

The principal object of the present invention is to provide novelapparatus for obtaining a varying amplitude signal from a series ofcoded impulses representing transmitted intelligence.

Another object of the invention is to employ a detector of any usualtype in a novel manner for the conversion of pulse width modulation intoa wave of varying amplitude.

Other and more specic objects of the invention will become apparent froma consideration of the following specification and claims in connectionwith the accompanying drawings, illustrating one form of the inventionin which:

Fig. 1 illustrates in block diagram form a television transmitter inwhich sound is transmitted in the form of variable width pulses.

Fig. 2 is a diagrammatic illustrative arrangement in accordance with theinvention for obtaining a wave of varying amplitude from a series ofwidth modulated pulses.

Figs. 3 through 8 are illustrative of the mannerv of obtaining a wave ofvarying amplitude by the apparatus of Fig. 2.

Fig. 1 of lthe accompanying drawings is similar to Fig. 1 of the abovementioned copending Fredendall et al. application and shows by way ofexample one method of obtaining width modulated impulses representingsound accompaniment in a television system. This arrangement is fullydescribedand claimed in the above noted application and is included herefor the sake of f completeness of disclosure. The arrangement forobtaining variable width dots representing picture intelligence isdisclosed in detail in the above mentioned Shore et al. patent andtherefore need not be described or explained herein in detail.

In Fig. 1, speech or other audible signals, which accompany image'orvideo signals appearing in a connection I0, are caused to influence asound signal device I2, which may be the usual type of microphone, andare then supplied to a sound amplifier and lter I4 whose output energyis directed to a modulator I6. The wave form of the derived signal fromthe modulator I6 is changed in an amplifier-limiter I'I and is appliedto a mixer I8 so as to be combined with video signals from theconnection IU. A square Wave pulse source I9, which may be amulti-vibrator. is timed by a source of control impulses 2 I, which mayoperate, for example, under control of the synchronizing impulses whichare employed in the usual manner to control the television scanner.Square wave pulses from the source I9 are converted by a wave shaper 22into triangular impulses which are applied to the modulator I6. The waveform of the signals is indicated in the usual manner in the output ofeach piece of apparatus. The output from the mixer I8 is supplied in anysuitable manner to the oscillator and modulator of a radio stationtransmitter or to a communication circuit of any kind.

In Fig. 2 the incoming signal is demodulated in any well known manner(not shown) so as to obtain the series of variable width dotsrepresenting intelligence as shown in Fig. 3 of the drawings. It will beunderstood that if variable width impulses are obtained in accordancewith the arrangement shown in the Shore patent, a simple demodulatingstep will be used to obtain these pulses from the radio frequencycarrier. If the series of impulses represents the sound accompanimenttransmitted along with television video signals in accordance with thearrangement shown in the above noted copending application, these pulseswill be separated from the video and the synchronizing signals afterdemodulation of the radio carrier, preferably in the manner disclosedand claimed in the said application.

This method comprises, briefly, an arrangement wherein a thermionicdevice is biased to cutoft except at times when the video signal is notpresent, and therefore the output of this electrical device representsreconstructed variable width impulses free of noise and interference andof the type shown by Fig. 3 of the accompanying drawings.

The variable width impulses derived either from' a sound or a facsimilesignal as in the Shore et al. patent, above noted, are applied to theinput of a differentiator 25. This diierentiator may comprise a/highpass filter or it may be a stage of ampliilcation in which the gridresistor and the input condenser serve as a high pass RC circuit. If theamplifier type of diierentiator is employed, the pulses may be ofnegative polarity so that after inversion, the initial peaks will be ofpositive polarity.

The output of the diierentiator 25 is shown in Fig. 4 of the drawingsand comprises narrow pulses 2l and 28 at the leading and trailing yedgesof the variable width pulses 26 of Fig. 3. The signal illustrated byFig. 3 is composed of a series of pulses characterized by leading edgeswhich are periodic in time, and trailing edges having positions whichare determined in accordance with the modulating wave. As an example,the width of the pulse may be proportional `to the instantaneous valueof the complex modul synchronizing means to a multivibrator or othersuitable type of square wave generator 29. The timed square waveimpulses 3l (Fig. 5) from the multivibrator 29 are applied to a waveshaper 32, which may be a triangular wave generator of any suitabletype.- Fig. 6 illustrates the output of the wave Shaper 32 whichcomprises triangularly shaped impulses 33. A The circuit elements 29 and32 may be similar to the elements I9 and 22 of Fig. 1, a specic type ofwhich is described by way of example in the above mentioned copendingapplication of Fredenall et al.

A clipper 36, which may be of any suitable type, eliminates the pulses21 and passes along only the pulses 28 amplitude limited in order toremove noise. The triangular wave 33 (Fig. 6) and the pulse wavecomposed of successive pulses 28 with their polarity reversed are addedin a mixer 3l, forming the composite Wave shown in Fig. 7. The portionof the wave of Fig. 'l below the line -z is removed by a clipper 39, andthe useful remaining signal illustrated in Fig. `8 constitutes a seriesof modulated pulses which may be detected by a peak detector or anamplitude detector 62 of any desired type. This detector may be aconventional diode detector, a grid-bias detector or a grid leakdetector. The output connection 43 of the detector B2 may be connectedto a sound reproducer E6. If the variable width pulses 26 are derived atthe transmitter from a representation of a picture or object in themanner described in the Shore et al. Patent No. 2,083,245 above referredto, the device M may be replaced by a picture recorder so thatshadedtone pictures may be reproduced.

If the variable width pulses 26 represent the sound accompanimenttransmitted along with television video signals in accordance with thearrangement shown in the above noted copending application, higherdelity sound can be obtained by increasing the number of scanning linesso that the number of pulses of sound energy per picture eld, assumingthe same eld repetition rate, will be higher, thus with vertical linescanning, the upper frequency register of the transmitted sound would beincreased in the illustradescribed herein by way of example arepossible, Without departing from the spirit and scope of the inventiondescribed herein, and it is desired that any and all of suchmodifications be considered Within the purview of the present inventiondeiined by the hereinafter appended claims.

Having now described -the invention, what is claimed and desired to besecured by Letters Patent is the following: A

1. The method of converting a series of width modulated impulses into .aseries of amplitude modulated impulses comprising the steps of producinga series of linearly varying impulses occurring intimed relationshipwith said series of Width modulated impulses, producing a series ofimpulses occurring in timed relationship with the end of a correspondingwidth modulated impulse, combining saidr linearly varying impulses withsaid series of impulses to produce impulses of varying amplitude, anddetectingv said impulses of varying amplitude to produce a series ofampli` tude modulated impulses.

2. The method of converting a series of width modulated impulses into aseries of amplitude varying output pulses comprising the steps ofproducing a series of impulses each having a steep front side and alinearly sloping end and of substantially constant amplitude occurringin timed relationship with said series of lwidth modulated impulses,producing a series of impulses occurring in timed relationship with theend of a corresponding width modulated impulse, combining said twoseries of impulses to produce impulses of varying amplitude, anddetecting said impulses of varying amplitude to produce a series ofamplitude modulated impulses.

3. The method of converting a series of Width modulated impulses into aseries of amplitude modulated impulses comprising the steps of producinga series of triangular impulses occurring in timed relationship withsaid series of width modulated impulses, producing a series of impulsesoccurring in timed relationship with the end of a corresponding widthmodulated impulse, combining said triangular impulses and said series ofimpulses to produce impulses of varying amplitude, and detecting saidimpulses of varying amplitude to produce a series of amplitude modulatedimpulses.

4. Apparatus for converting a series of Width modulated impulses into aseries of amplitude varying output pulses comprising means to produce aseries of linearly varying impulses in timed relationship with saidseries of width modulated impulses, means for producing impulses intimed relationship with the end of each width modulated impulse, meansfor combining said linearly varying impulses and said last namedimpulses, means to suppress a portion of said combined impulses, andwave detecting means for producing a series of amplitude varying outputpulses.

5. Apparatus for converting a series of Width modulated impulses into aseries of amplitude varying output pulses comprising means to produce aseries of impulses each` having a steep front side and a linearlysloping end and of substantially constant amplitude in timedrelationship with said series of width modulated impulses. means forproducing impulses in timed relationship with the end of each widthmodulated mpulse, means for combining said linearly sloping end impulsesand said last named impulses, means to suppress a portion of saidcombined impulses, and Wave detecting means for producing a series ofamplitude varying output pulses.

lated impulse, means i'or combining said triangular impulses and saidlast named impulses, means to suppress the triangular portion of saidimpulses, and wave detecting means for producing a 5 series of amplitudevarying output pulses.

GORDON L. FREDENDALL

